java.lang.NullPointerexception

Since being forced to update to the new launcher, I can't play on any server. When I try to join a server, I get the message in the summary. I can still do single-player, but no server. I see the server list, how many people are playing, but click to join & get the summary message. I've updated Windows 10, all my drivers, my Java, reinstalled Minecraft, nothing works. I don't know what you'd need to reproduce it. Is there a way to go back to the old launcher, since I had no problems with it whatsoever?